Spelling suggestions: "subject:"fieldeffect transistors."" "subject:"fields:effect transistors.""
121 |
Contrôle de la formation de nanostructures dans les films minces de polymères conjuguésDerue, Gwennaelle G.S.Y.T. 24 September 2008 (has links)
Notre recherche se base sur la structuration des polymères conjugués qui présentent des propriétés optiques et électroniques intéressantes en raison de leur structure moléculaire intrinsèque. En effet, la structure des polymères conjugués se compose d’une alternance de simples et de doubles liaisons donnant lieu à une délocalisation des électrons le long des chaînes. Cette conjugaison est à l’origine de leurs propriétés de luminescence et de leur caractère semi-conducteur. Ces polymères sont couramment utilisés dans des dispositifs électroniques où ils jouent le rôle de composant actif. Le fonctionnement de ces dispositifs repose sur la capacité des charges à se déplacer le long des chaînes (processus intramoléculaire) et d'une chaîne à l'autre (processus intermoléculaire) et par conséquent, ces propriétés de transport dépendent de l’arrangement des chaînes polymères dans le solide, qui lui-même découle des interactions supramoléculaires. Il est donc impératif de maîtriser ces interactions et d’étudier l’influence qu’elles ont sur les performances de tels dispositifs électroniques. C’est précisément sur ce point que porte notre travail : étudier et contrôler la formation de nanostructures en termes de dimensions, de forme et de localisation, en appliquant une contrainte physique extérieure à un film de polymère conjugué.
Le polymère conjugué sur lequel notre étude se base principalement est le poly(3-hexylthiophène), P3HT. Ce polymère est semi-cristallin et possède une mobilité de charge élevée (0.18 cm2/V.s), ce qui en fait un très bon candidat en tant que composant actif dans les transistors à effet de champ.
Nous avons, dans le cadre de notre recherche, étudié la structuration de films minces de P3HT, réalisée par l’application de contraintes physiques extérieures. L’utilisation d’une pointe de microscope à force atomique travaillant en mode contact permet de déformer plastiquement la surface polymère en créant des structures périodiques en surface des films mais elle permet, en outre, d’orienter les chaînes polymères dans la direction de passage de la pointe. Différents paramètres expérimentaux ont été étudiées comme par exemple, la résolution choisie pendant l’expérience, le nombre de passage effectués par la pointe ou encore l’angle avec lequel la pointe structure le film polymère. Nous avons également démontré que cette technique, appliquée au canal polymère d’un transistor à effet de champ, permet d’améliorer les propriétés électriques du P3HT et par conséquent, d’augmenter les performances du dispositif électronique.
Nous avons utilisé une autre méthode, dite de « lithographie douce », afin de structurer le P3HT. Cette technique présente l’avantage de « façonner » le polymère lorsqu’il se trouve en solution et ne nécessite donc pas la formation préalable d’un film. Elle consiste à déposer une goutte de solution polymère sur un substrat, à l’entrée de canaux micrométriques de PDMS; l’écoulement de la solution polymère, qui se fait par capillarité dans les canaux, est donc confiné. Le solvant va ensuite s’évaporer et il reste alors, sur le substrat, un dépôt polymère qui est la réplique négative des canaux de PDMS. L’analyse du dépôt polymère formé grâce à cette méthode révèle, comme c’était le cas pour la technique précédente, une orientation des chaînes polymères au sein des canaux.
Dans la dernière partie de ce travail, nous avons étudié le dopage de films fibrillaires de P3HT. L'étude de la morphologie des films dopés montre que la structure fibrillaire est conservée, avec une légère augmentation de la largeur des fibrilles. Cette augmentation résulte d'un déplacement des chaînes polymères les unes par rapport aux autres dans l'axe du squelette conjugué afin de laisser des espaces vacants pour accueillir les contre-ions dans le réseau polymère. Les mesures électriques des films dopés montrent un accroissement très important de la conductivité du polymère. On observe une augmentation de six ordres de grandeur entre les conductivités d'un film neutre et dopé.
|
122 |
Growth, fabrication and testing of pseudomorphic P-channel GaAs/InGaAs/AlGaAs MODFETSSchulte, Donald W. 14 August 1992 (has links)
This thesis reports on the growth and characterization of p-type
pseudomorphic A1GaAs /InGaAs /GaAs modulation doped field effect transistor
(MODFET) structures. A series of different p-type MODFET structures were grown
with a systematic variation of the indium mole fraction and quantum well width of
the InGaAs channel region. Extensive characterization of these samples using van
der Pauw Hall and photoluminescence measurements showed clear trends in carrier
mobility and quantum well quality with respect to the structure of the InGaAs region.
From this an optimal indium mole fraction and quantum well width were obtained.
Subsequent to material characterization, MODFET devices were fabricated
and characterized. The measured DC device performance was reasonable and
suggests that high quality p-type MODFETS should be obtainable with a properly
optimized device structure and fabrication process. / Graduation date: 1993
|
123 |
Hot electron effects in N-channel MOSFET'sOr, Siu-shun Burnette 08 November 1991 (has links)
The purpose of this work is to develop a new model for LDD
n-MOSFET degradation in drain current under long-term AC use
conditions for lifetime projection which includes a self-limiting
effect in the hot-electron induced device degradation.
Experimental results on LDD n-channel MOSFETs shows that the
maximum drain current degradation is a function of the AC
average substrate current under the various AC stress conditions
but not a function of frequency or waveforms or different
measurement configurations. An empirical model is constructed
for circuit applications. It is verified that the self-limiting in drain
current is due to the thermal re-emission of a trapped-hot-electron
in the oxide. Results show that self-heating during AC
stress releases trapped electrons, which in turn limits the
maximum amount of drain current degradation. Moreover,
tunneling to and from traps model is employed to visualize the
internal mechanism of thermal recovery of electrons under
different bias conditions. Although the LDD device structure can
reduce the hot electron effect, various processing technologies can
also affect the device reliability. A carbon doped LDD device with
the first and the second level metal and passivation layer but
without any final anneal shows that a significant reduction in the
shifts of the threshold voltage of MOSFETs with time can be
achieved. However, the long-term reliability projection of nMOSFETs
based on DC stress tests alone is shown to be overly
pessimistic. / Graduation date: 1992
|
124 |
A P-well GaAs MESFET technologyCanfield, Philip C. 02 August 1990 (has links)
The semiconductor gallium arsenide (GaAs) has many potential
advantages over the more widely used semiconductor silicon (Si).
These include higher low field mobility, semi-insulating substrates,
a direct band-gap, and greater radiation hardness. All these
advantages offer distinct opportunities for implementation of new
circuit functions or extension of the operating conditions of similar
circuits in silicon based technology. However, full exploitation of
these advantages has not been realized. This study examines the
limitations imposed on conventional GaAs metal-semiconductor field
effect transistor (MESFET) technology by deviations of the semi-insulating
substrate material from ideal behavior. The interaction
of the active device with defects in the semi-insulating GaAs
substrate is examined and the resulting deviations in MESFET
performance from ideal behavior are analyzed.
A p-well MESFET technology is successfully implemented which
acts to shield the active device from defects in the substrate.
Improvements in the operating characteristics include elimination of
drain current transients with long time constants, elimination of the
frequency dependence of g[subscript ds] at low frequencies, and the elimination of
sidegating. These results demonstrate that control of the channel to
substrate junction results in a dramatic improvement in the
functionality of the GaAs MESFET. The p-well MESFET RF
characteristics are examined for different p-well doping levels.
Performance comparable with the conventional GaAs MESFET technology
is demonstrated. Results indicate that optimization of the p-well
MESFET doping levels will result in devices with uniform
characteristics from DC to the highest operating frequency. / Graduation date: 1991
|
125 |
Analysis and modeling of GaAs MESFET's for linear integrated circuit designLee, Mankoo 31 May 1990 (has links)
A complete Gallium Arsenide Metal Semiconconductor
Field Effect Transistor (GaAs MESFET) model including deep-level
trap effects has been developed, which is far more
accurate than previous equivalent circuit models, for high-speed
applications in linear integrated circuit design.
A new self-backgating GaAs MESFET model, which can
simulate low frequency anomalies, is presented by including
deep-level trap effects which cause transconductance
reduction and the output conductance and the saturation
drain current to increase with the applied signal frequency.
This model has been incorporated into PSPICE and includes a
time dependent I-V curve model, a capacitance model, a
subthreshold current model, an RC network describing the
effective substrate-induced capacitance and resistance, and
a switching resistance providing device symmetry.
An analytical approach is used to derive capacitances
which depend on Vgs and Vds and is one which also includes
the channel/substrate junction modulation by the self
backgating effect. A subthreshold current model is
analytically derived by the mobile charge density from the
parabolic potential distribution in the cut-off region. Sparameter
errors between previous models and measured data
in conventional GaAs MESFET's have been reduced by including
a transit time delay in the transconductances, gm and gds,
by the second order Bessel polynomial approximation. As a
convenient extraction method, a new circuit configuration is
also proposed for extracting simulated S-parameters which
accurately predict measured data. Also, a large-signal GaAs
MESFET model for performing nonlinear microwave circuit
simulations is described.
As a linear IC design vehicle for demonstrating the
utility of the model, a 3-stage GaAs operational amplifier
has been designed and also has been fabricated with results
of a 35 dB open-loop gain at high frequencies and a 4 GHz
gain bandwidth product by a conventional half micron MESFET
technology. Using this new model, the low frequency
anomalies of the GaAs amplifier such as a gain roll-off, a
phase notch, and an output current lag are more accurately
predicted than with any other previous model.
This new self-backgating GaAs MESFET model, which
provides accurate voltage dependent capacitances, frequency
dependent output conductance, and transit time delay
dependent transconductances, can be used to simulate low
frequency effects in GaAs linear integrated circuit design. / Graduation date: 1991
|
126 |
Nuclear quadrupole resonance spectrometer using field-effect transistorsCraig, Ronald E. 03 June 2011 (has links)
This thesis includes elementary introductions to nuclear quadrupole resonance (NQR) detection and fieldeffect transistors (PET). The construction and operation of the FET-NQR detector, as originally designed by Viswanathan, Viswanathan and Sane and published in Rev. Sci. Instr. 39,472 (1968), is discussed extensively. The thesis also contains a step by step discussion of the construction of an alternate PET-N'QP detector. Although the alternate detector never functioned properly, the information gathered would aid anyone desiring to design and construct a new NQR detector.Ball State UniversityMuncie, IN 47306
|
127 |
Effects of the Dielectric Environment on the Electrical Properties of GrapheneAnicic, Rastko January 2013 (has links)
This thesis provides the study of graphene’s electrostatic interaction with the substrate surrounding it. Mathematical models based on current experimental configurations of graphene field-effect transistors (FET) are developed and analyzed. The conductivity and mobility of charge carriers in graphene are examined in the presence of impurities trapped in the substrate near graphene. The
impurities encompass a wide range of possible structures and parameters, including different types of impurities, their distance from graphene, and the spatial correlation between them. Furthermore, we extend our models to analyze the influence of impurities on the fluctuations of the electrostatic
potential and the charge carrier density in the plane of graphene. The results of our mathematical
models are compared with current experimental results in the literature.
|
128 |
Quantum effects in MOSFETs /Ontalus, Viorel, January 2000 (has links)
Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 132-136).
|
129 |
Design and fabrication of 4H silicon carbide MOSFETSWu, Jian. January 2009 (has links)
Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Electrical and Computer Engineering." Includes bibliographical references (p. 151-156).
|
130 |
Physical model enhancement and exploration of bandgap engineering in novel sub-100nm pMOSFETs /Ouyang, Qiqing Christine, January 2000 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 129-145). Available also in a digital version from Dissertation Abstracts.
|
Page generated in 0.0627 seconds